"The simplified texture classifications are derived from measured soil thicknesses taken from archive borehole records held by BGS (see the BGS Soil-sample Depth dataset in the map viewer: http://mapapps2.bgs.ac.uk/ukso/home.html?layers=SamplesDepth). The thicknesses are compared and collated with the expected engineering strength classification of their underlying soil-parent material type to show a map of distribution of the classes; expert judgment has been used to estimate a thickness class where borehole data is not available). Note that the map uses combinations of terms that refer to: Deep soils, Intermediate soils and Shallow soils (see table below).

As a rule of thumb, these categories are based on the ability to manually dig (with a spade) without being hindered by a substrate that is too strong to excavate (i.e. layers of solid rock, dense gravel, or very stiff clays). An example of a deep soil would be one developed over unconsolidated, clayey Quaternary deposits, and an example of a shallow soil would be one found in areas underlain by chalk or limestone. Users should note that land management practices and natural weathering and accumulation (or erosion) processes of soil materials play a significant role in controlling soil thickness (it has not been possible to factor in these influences within the scope of this dataset) and so the classes shown in this dataset should be regarded as 'indicative'."